ENGINE (DIAGNOSTICS)(H4SO) > Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0851 NEUTRAL SWITCH INPUT CIRCUIT LOW (MT MODEL)

ENGINE (DIAGNOSTICS)(H4SO) > Diagnostic Procedure with Diagnostic Trouble Code (DTC)

DTC P0851 NEUTRAL SWITCH INPUT CIRCUIT LOW (MT MODEL)

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.

TROUBLE SYMPTOM:

Erroneous idling

CAUTION:

After repairing or replacing the defective part, perform the Clear Memory Mode and Inspection Mode .

WIRING DIAGRAM:

STEP	CHECK	YES	NO
1.CHECK INPUT SIGNAL OF ECM. 1) Turn the ignition switch to ON. 2) Place the shift lever in neutral. 3) Measure the voltage between ECM and chassis ground. Connector & terminal (B136) No. 31 (+) — Chassis ground (−):	Is the voltage less than 1 V?
2.CHECK INPUT SIGNAL OF ECM. 1) Place the shift lever in a position except for neutral. 2) Measure the voltage between ECM and chassis ground. Connector & terminal (B136) No. 31 (+) — Chassis ground (−):	Is the voltage 10 V or more?
3.CHECK POOR CONTACT. Check poor contact of ECM connector.	Is there poor contact in ECM connector?	Repair the poor contact of ECM connector.	Contact your SUBARU distributor service.
4.CHECK NEUTRAL POSITION SWITCH. 1) Turn the ignition switch to OFF. 2) Disconnect the connector from the transmission harness. 3) Place the shift lever in neutral. 4) Measure the resistance between transmission harness and connector terminals. Connector & terminal (T2) No. 1 — No. 2:	Is the resistance less than 1 Ω?		Repair the open circuit in transmission harness, or replace the neutral position switch.
5.CHECK NEUTRAL POSITION SWITCH. 1) Place the shift lever in a position except for neutral. 2) Measure the resistance between transmission harness connector terminals.	Is the resistance 1 MΩ or more?		Repair the short circuit in transmission harness, or replace the neutral position switch.
6.CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. Measure the resistance between ECM and chassis ground. Connector & terminal (B136) No. 31 — Chassis ground:	Is the resistance 1 MΩ or more?		Repair the ground short circuit of harness between ECM and transmission harness connector.
7.CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. 1) Disconnect the connectors from the ECM. 2) Measure the resistance of harness between ECM and transmission harness connector. Connector & terminal (B136) No. 31 — (B25) No. 2:	Is the resistance less than 1 Ω?		Repair the open circuit of harness between ECM and transmission harness connector.
8.CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. Measure the resistance of harness between transmission harness connector and ECM. Connector & terminal (B25) No. 1— (B136) No. 6:	Is the resistance less than 5 Ω?		Repair the open circuit between transmission harness connector and ECM terminal.
9.CHECK POOR CONTACT. Check poor contact of transmission harness connector.	Is there poor contact in transmission harness connector?	Repair the poor contact of transmission harness connector.	Contact your SUBARU distributor service.